1. Field of the Invention
The present invention relates to a compatible optical pickup apparatus and method for recording and reproducing information with respect to optical recording media in different formats. More particularly, the present invention relates to a compatible optical pickup apparatus and method for using a beam shaping prism having an improved structure.
2. Description of the Related Art
In general, a compatible optical pickup apparatus can record and reproduce information with respect to optical recording media in different formats, for example, a Digital Video Disk (DVD) and a Compact Disk (CD).
Referring to FIG. 1, a conventional compatible optical pickup apparatus includes an optical module 11 for emitting light having a predetermined wavelength and receiving light reflected from an optical recording medium D, a second light source 21 for emitting light having a wavelength different from the light source module 11, a beam shaping prism 30 for changing a proceeding path of incident light and correcting an incident beam, a beam splitter 41 for changing a proceeding path of incident light, an objective lens 43 for focusing incident light and forming a light spot on the optical recording medium D, and a main photodetector 49 for receiving incident light that is reflected from the optical recording medium D and passes through the beam splitter 41 and the beam shaping prism 30 and detecting an information signal and an error signal.
The light source module 11 is a module in which a first light source (not shown), a photodetector (not shown) that is arranged proximally to the first light source, and a holographic optical element 12 are integrally formed. Light emitted from the first light source transmits straight and proceeds toward the optical recording medium D. Light reflected from the optical recording medium D is diffracted by the holographic optical element 12 so as to be formed on the photodetector.
A first grating 15 for diffracting and transmitting the light emitted from the first light source into a 0th order beam, ±1st order beams, ±2nd order beams, and so on, and a first coupling lens 13 primarily converging divergent light emitted from the first light source, are provided in an optical path between the light source module 11 and the beam splitter 41. Most of the light emitted from the first light source and proceeds toward the beam splitter 41 and proceeds toward the optical recording medium D while part of the light is reflected by the beam splitter 41 and received by a first monitoring photodetector 17. The optical power of the first light source can be estimated from the amount of light received by the first monitoring photodetector 17, which enables control of the optical power of the first light source.
The second light source 21 is formed of a semiconductor laser that emits light having a relatively short wavelength compared to the first light source.
Referring to FIG. 2 in the second light source 21, a cap 213 having a window 215 that a laser beam transmits from is provided on a base 211. A mount 212 is provided on the base 211 and a semiconductor laser 217 for emitting a laser beam having a predetermined wavelength from the opposite side surfaces is installed on a side wall of the mount 212.
Referring to FIG. 3, the laser beam emitted from a predetermined position of an active layer 217a of the semiconductor laser 217 maintains an oval sectional shape. This is due to a phenomenon in which the laser beam is diffracted differently in each of a thickness direction (Y-axis direction) of the active layer 217a and a widthwise direction (X-axis direction) perpendicular thereto because the size of an outlet through which the laser beam is emitted is different according to the thickness direction and the widthwise direction. The laser beam in the thickness direction is apparently emitted from the front side of the semiconductor laser 217 and the laser beam in the widthwise direction is apparently emitted from a position located in the rear as much as ΔZ from the front side of the semiconductor laser. The difference in distance ΔZ is referred to as astigmatism. In FIG. 2, θΠ denotes an angle of the laser beam spreading in the widthwise direction and θ⊥ denotes an angle of the laser beam spreading in the vertical direction.
The optical pickup apparatus adopting the semiconductor laser has a problem of astigmatism generated due to the structural property of a light source. That is, when the astigmatism is large, a jitter property deteriorates during reproduction of a signal reflected from the optical recording medium D through the main photodetector of the optical pickup apparatus so that signal detection is severely affected. Jitter refers to a phenomenon in which deviation of a signal increases when a pit recorded on the optical recording medium is formed poorly or the shape of the light spot formed on the optical recording medium is asymmetrical. Such a phenomenon has a large affect when information is stored in the optical recording medium. Thus, in order to use the light source module in the optical pickup apparatus for recording, beam shaping is necessary.
Referring now to FIG. 1, the beam shaping prism 30 shapes incident light having an oval profile so that a light spot having a circular profile is formed on the optical recording medium D. By shaping the beam, information can be recorded with respect to the optical recording medium D using the light emitted from the second light source 21.
A second coupling lens 23 for concentrating incident divergent light and a second grating 25 diffracting and transmitting incident light are arranged in the optical path between the second light source 21 and the beam shaping prism 30.
The beam shaping prism 30 has an incident surface 31 on which the light emitted from the second light source 21 is incident, a reflective surface 32 on which the incident light is reflected, and an output reflective surface 33 on which the light reflected from the reflective surface 32 is transmitted in a straight direction and the light incident from the optical recording medium D is reflected toward the main photodetector 49. Thus, the light emitted from the second light source 21 and transmitting the output reflective surface 33 is reflected by the beam splitter 41 and proceeds toward the optical recording medium D.
A second monitoring photodetector 27 is arranged at a predetermined position facing the incident surface 31. The second monitoring photodetector 27 receives part of the light emitted from the second light source 21 and reflected from the incident surface 31 and detects the optical power of the second light source 21.
A collimating lens 45 for concentrating incident light and a sensor lens 47 for adjusting the size of incident light and changing a focal position of the incident light are arranged on the optical path between the output reflective surface 33 and the main photodetector 49.
The compatible optical pickup apparatus configured as above can record and reproduce information with respect to optical recording media in different formats. Since a plurality of optical elements including the beam shaping prism are used for recording, manufacturing costs increase and the structure becomes complicated so that the size of the optical pickup apparatus increases and the number of work steps increases. Furthermore, by adopting the beam shaping prism, when the optical pickup apparatus is operated at a high temperature, the optical axis may deviate.